Additional training can take many forms. Seminars, open rolls, and tournaments are just a few examples. Why are these events so important to your training?
They Keep Things Fresh
As you train and start working with others, you start figuring things out about your training partners. We all have habits, and the more you work with familiar people, the more you can anticipate just how he or she will react. By training with new people, you can better tell if your techniques are working properly. A technique will work differently on someone who has no idea it's coming.
They Put Things Into Perspective
Maybe you're the biggest guy in class. Maybe you're the smallest. Maybe you're the oldest. Maybe you're the youngest. By traveling to another school, you can seek out others with similar or different body types than you're used to. I'm used to working with people a lot bigger than me in our classes. At first I was getting a little discouraged because it seemed like everyone was better-- Until I went to another school that had several women my size. I held my own! Suddenly I didn't seem to be doing nearly as badly as I had been thinking I was.
They Prevent "Martial Inbreeding"
This is a term I use for when people substitute anticipation/expectations for technique. In other words, is something working because it's legit? Or because Sensei says it will work and it's working for everyone else? Other instructors and high ranking individuals may have new ways of looking at things or interpreting techniques. By going out and experiencing new ideas - even if you don't agree with them - you keep adding tidbits of understanding and knowledge to your belt. This keeps your martial world growing, expanding, and evolving.
There are so many more reasons to venture outside your school walls. I'll tackle more in another post.